Add Show in File System View to project tree context menu

That opens the selected file/path in the file system view.
Behaves the same as the navigation view shortcut + syncing with the
selected file.

It would be nice to have that at other places too, but this requires
moving the file system view to Core plugin first.

Change-Id: Icc6d1041156d97f5d2bda43a3501758f06fe80aa
Reviewed-by: Cristian Adam <cristian.adam@qt.io>

src/plugins/coreplugin/fileutils.h

@@ -46,6 +46,7 @@ struct CORE_EXPORT FileUtils
     static void openTerminal(const Utils::FilePath &path);
     static void openTerminal(const Utils::FilePath &path, const Utils::Environment &env);
     static QString msgFindInDirectory();
+    static QString msgFileSystemAction();
     // Platform-dependent action descriptions
     static QString msgGraphicalShellAction();
     static QString msgTerminalHereAction();